Control mechanisms have long been used to control the flow of fluid under pressure, through guns, in the water blasting art. Disposal of the excess and the used water has become a problem, to the environment. Applicant""s assignee hereof, is also the owner of U.S. Pat. No. 5,349,982, which is directed to some of the features possessed by this invention, such as quick maintenance. However, said prior patent""s gun was xe2x80x9cwet,xe2x80x9d i.e., it exhausted excess fluids through a dump tube. Applicant""s need is to duplicate the control, yet keep it xe2x80x9cdry,xe2x80x9d i.e., no exhaustion into the nearby environment.
Hand held Control Guns used in water blasting applications fall into two basic categories, either xe2x80x9cDump Typexe2x80x9d or xe2x80x9cDry Shut-off Type.xe2x80x9d The dump type is the gun/control mechanism for which we obtained our previous patent (U.S. Pat. No. 5,349,982), and it dumps water at low pressure through a valve when a trigger is released. This is a very simple device, which has the disadvantages of being wasteful of water, and also of tending to increase the clean-up effort required, because the water, which is dumped, usually mixes with debris being removed from the surfaces being cleaned. The dry shut-off type gun does not dump water when the trigger is released, it simply cuts off the flow at the gun, and the unused flow of water is diverted to the inlet side of the pump, usually into a header tank (a reservoir tank from which the pump can take its supply of water). The diversion of the flow is achieved by means of a separate xe2x80x9cUnloader Valve,xe2x80x9d which is not part of the current invention, but is a type of pressure relief valve. When flow is blocked at the gun, the pressure in the system tends to increase to levels above a chosen operating range. The excess pressure is released by the unloader valve, which is spring biased towards a closed position. The valve is moved off its seat by the overpressure, which releases some of the flow, thereby reducing the pressure to a level, which has been preset by adjusting the force on the spring.
The valve control mechanism, which is the subject of the current invention, bears a family resemblance to the dump valve being a similar type of device. When a trigger is pulled the valve is lifted off its seat allowing water to pass through the seat area and to flow down the barrel of the gun and exit at high pressure through a nozzle. When the trigger is released, the valve reseats itself and water ceases to flow from the nozzle and no further water is seen in the vicinity of the gun. Dry shut-off guns of many different formats are available on the market, but the major advantage of this design is the ease of overhaul of the gun by combining all of the wear components into a single cartridge, which can be replaced in the field very easily.
Since we received our original patent on the dump-type cartridge, there have been some changes in the external appearance of the guns, but the principles of their operation have remained unchanged. The cartridge is now mounted vertically in the gun, and the extension of the trigger now pivots below the gun and swings upwards to operate the valve. This applies to the dump gun and also to the dry shut-off gun, which will be described below.